Abstract : A three year research effort on 'A Fundamental Study of Compressibility Effects on Dynamic Stall of Fixed and Adaptive Airfoils' was initiated in 1994. The research led to an understanding of: some of the key mechanisms of compressible dynamic stall including when the flow over the airfoil is transonic; the Reynolds number effects which strongly after the detailed flow physics making extension of laboratory results to full-scale conditions extremely challenging, and the role of transition and a need to model it properly in computations. Further, the results demonstrated the major role of the airfoil leading edge curvature in producing the flow gradients that are responsible for dynamic stall onset, which enabled the development of a dynamically developing leading edge (DDLE) airfoil for effective flow control by modifying the vorticity field in the flow. The significant results of the effort are summarized in this report.